1. Field of Invention
The present invention relates to a pixel structure and repair method thereof. More particularly, the present invention relates to a pixel structure and repair method thereof, which can improve the display quality of the liquid crystal display panel.
2. Description of Related Art
Nowadays, the development of multimedia technology can be mostly attributed to the improvement of the semiconductor devices or the display devices. For the display devices, the thin film transistor liquid crystal displays (TFT-LCD), with advantages such as high image quality, high spatial utilization, low power consumption, and low radiation, etc., have gradually become the main stream product in the market.
The typical TFT-LCD mainly includes a thin film transistor array substrate, an opposite substrate, and a liquid crystal layer disposed between the two substrates. Wherein, the thin film transistor array substrate mainly includes a substrate, thin film transistors arranged on the substrate in an array, pixel electrodes, scan lines, and data lines. In general, the scan line and the data line can transmit a signal into the corresponding pixel structure.
FIG. 1A is a partial schematic view of a conventional pixel structure, and FIG. 1B is a cross-sectional schematic view of FIG. 1A along line A-A′. Please refer to FIG. 1A and FIG. 1B simultaneously. The conventional pixel structure 120 is made on a substrate 110. The pixel structure 120 mainly includes a thin film transistor 122, a pixel electrode 124, a scan line 126 and a data line 128. Wherein, the thin film transistor 122 is electrically connected to the pixel electrode 124, and the thin film transistor 122 has a bottom gate. As shown in FIG. 1B, the thin film transistor 122, disposed on the substrate 110, mainly includes a gate 122a, a channel layer 122b, a source 122c, and a drain 122d, wherein the drain 122d of the thin film transistor 122 is electrically connected to the pixel electrode 124 through a contact hole H. As shown in FIG. 1A, a suitable voltage can be transmitted to the thin film transistor 122 by the scan line 126 and the data line 128, and the voltage is transmitted to the pixel electrode 124 through the thin film transistor 122.
Note that, as the gate 122a and the drain 122d are partially overlapped, a parasitic capacitance Cgd may be generated between the gate 122a and the drain 122d. In FIG. 1A, the reference number 10 marks the overlapping area between the drain 122d and the gate 122a. In addition, the capacitor value of the parasitic capacitance Cgd has positive relation to the area of the overlapping area 10. The parasitic capacitance Cgd may cause RC delay; accordingly, the feed-through voltage of the charged pixel electrode 124 can not reach the predefined voltage. That is, the feed-through voltage of the charged pixel electrode 124 may vary according to the capacitor value of the parasitic capacitance Cgd.
In the fabrication of the pixel structure 120, the overlapping area of each gate 122a and drain 122d should be equal. However, in the fabrication of the thin film transistor array substrate, there would be the so-called overlay shift in the photolithograph process of each photomask due to the alignment error of the photomask or the tremble of the machine, etc., and the overlay shift may be more serious in the fabrication of a large panel. In addition, when the overlay shift between the gate 122a and the drain 122d in partial areas is too large, the difference between the capacitor value of the parasitic capacitor Cgd in the area and the capacitor value of the parasitic capacitor Cgd in other area is too much, resulting in the mura of feed-through voltage in each area. Accordingly, the feed-through voltage of the charged pixel electrode 124 does not reach the predefined voltage, so that the display mura may occur in the liquid crystal display panel using the pixel structure 120.
In addition, in the fabrication process of the thin film transistor array substrate, a part of the pixel structure 120 may inevitably have defects and can not work normally. The defects may cause bright spots or bright lines in the liquid crystal display panel when displaying images.